Adobe 23101335 User Guide - Page 122
L*a*b model, Bitmap mode, Grayscale mode, the Color Settings dialog box. See About
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112 CHAPTER 3 Working with Color Although CMYK is a standard color model, the exact range of colors represented can vary, depending on the press and printing conditions. Photoshop's CMYK mode varies according to the working space setting that you have specified in the Color Settings dialog box. (See "About working spaces" on page 125.) L*a*b model The L*a*b color model is based on the model proposed by the Commission Internationale d'Eclairage (CIE) in 1931 as an international standard for color measurement. In 1976, this model was refined and named CIE L*a*b. L*a*b color is designed to be device independent, creating consistent color regardless of the device (such as a monitor, printer, computer, or scanner) used to create or output the image. L*a*b color consists of a luminance or lightness component (L) and two chromatic components: the a component (from green to red) and the b component (from blue to yellow). A B C D A. Luminance=100 (white) B. Green to red component C. Blue to yellow component D. Luminance=0 (black) Lab mode In Photoshop, Lab mode (the asterisks are dropped from the name) has a lightness component (L) that can range from 0 to 100. The a component (green-red axis) and the b component (blue-yellow axis) can range from +120 to -120. You can use Lab mode to work with Photo CD images, edit the luminance and the color values in an image independently, move images between systems, and print to PostScript® Level 2 and Level 3 printers. To print Lab images to other color PostScript devices, convert to CMYK first. Lab color is the intermediate color model Photoshop uses when converting from one color mode to another. Bitmap mode This mode uses one of two color values (black or white) to represent the pixels in an image. Images in Bitmap mode are called bitmapped 1-bit images because they have a bit depth of 1. For more information, see "Specifying 8-bit color display (Photoshop)" in online Help. Grayscale mode This mode uses up to 256 shades of gray. Every pixel of a grayscale image has a brightness value ranging from 0 (black) to 255 (white). Grayscale values can also be measured as percentages of black ink coverage (0% is equal to white, 100% to black). Images produced using black-and-white or grayscale scanners typically are displayed in Grayscale mode.